I caught this great egret flying overhead with my Nikon D4 and the new 800mm f5.6 Nikkor with its 1.25x teleconverter. The bird was so close that I couldn’t even get all of it in frame. The camera lens combination is incredibly fast focusing. Without it, I doubt this shot would have been possible.  This species flies at about 25mph and the bird was moving across my field of view. The shot was taken from about 30 feet away at 1/64ooth of a second on a heavily overcast day.